Buildings constructed from concrete panels fall broadly into two categories, namely those constructed using tilt-up concrete panels and those using pre-cast concrete panels.
Tilt-up concrete panels are cast on site, usually on the concrete slab which will eventually form the floor of the finished building. The panels are formed individually, often being stacked cast when the dimensions of individual panels permit. The organization of this process requires much planning as the cast must reflect the appropriate lifting order of the panels. The casting of panels on site is a labor-intensive endeavor and is subject to usual on-site problems. Once cured, the panels are lifted into place by use of a crane which is attached to lifting anchors cast into the panels. The panels are lifted from their horizontal as cast position to their final vertical position and during this process the stresses induced in the panel are often those governing the extent of reinforcement required in the panel.
Pre-cast concrete panels, by comparison, eliminate many of these on-site problems by casting individual panels in a factory environment. Once cured, the panels are rotated on a casting bed through 90° from the horizontal position so the panel is lying along its major axis. An overhead crane then lifts the panel from its casting bed, using lifting anchors cast into the panel, and places the panel onto a flat-bed truck for transport to site. On site, a crane is used to lift the panel into position as a part of a wall of a building. The size of pre-cast panels is restricted by transport requirements and, as such, they are usually a lot smaller than tilt-up panels cast on site and are generally not large enough to support a roof structure. From the above it can be seen that larger panels are normally cast on site as they are too large and heavy to transport, while smaller panels are pre-cast and then transported to site and erected. It would be economically advantageous to be able to precast larger panels. However, to lift a large panel from a transport truck, the panel has to be spun from its transporting position (lying on one long side) to its installation position (standing vertical). One known way of achieving this is to use a crane with a complicated spinning rig. Another method is to use two cranes. Both methods are time consuming, expensive and can be dangerous to operators.